Analysis of the 10 July 2002 St. Cloud, Minnesota Flash Flood Event Justin Turcotte 5 April 2003

Images of the Flood Images from St. Cloud Times, 11 July 2002

What Happened?  Significant amount of rain in a very short amount of time  Rain fell on already saturated ground  SCSU (near STC): 4.29”, 2.70” within 1hr 45 min  AXN: 3.52”, Inch an hour for three hours From St. Cloud Times 2002

Month’s Worth of Rain in One Day  The St. Cloud area average July precipitation is 3.38”  Event followed above average June precipitation  Saturated soil

METAR from Alexandria, MN  KAXN Z AUTO 08017G25KT 3/4SM +TSRA BR BKN007 OVC019 19/19 A3000 RMK AO2 PK WND 09026/0817 LTG DSNT ALQDS TSE0757B05 SLP153 P T  KAXN Z AUTO 09013G21KT 1 1/4SM +TSRA BR OVC007 19/18 A3000 RMK AO2 LTG DSNT ALQDS SLP151 P0119 T  KAXN Z AUTO 10016G23KT 10SM BKN033 BKN060 OVC100 19/18 A2999 RMK AO2 PK WND 10029/1032 LTG DSNT E TSE38RAE44 SLP149 P0098 T

Soil Conditions June/July Images from National Climatic Data Center (NCDC)

The K-Index  KI = (T850mb- T500mb) + Td850mb -(T700mb - Td700mb).  0-15 No thunderstorms  Thunderstorms unlikely  Isolated thunderstorms  Widely scattered thunderstorms  Numerous thunderstorms  Thunderstorms very likely  % chance of thunderstorms  MPX 1200z Sounding K = 38 (bet the farm!) from Sturtevant 1995

Type “F”: Northwest Flow Ridge Riders

 r.edu/case-selection/ r.edu/case-selection/ r.edu/case-selection/  Surface  Radar  Satellite

Mosquito Breeding Ground Land of 10,000++ Lakes from St. Cloud Times 2002

Storm Reports July

Summary  Abundant moisture throughout atmosphere  Moisture convergence over area  Strong 500 hPa vorticity advection  Upper-air divergence  Slow moving storms  Extreme intensity rainfall rates  Saturated ground   FLOOD

 Why did the lady go out doors with her purse open? Because she expected some change in the weather.